The present invention is generally directed to linear voice coil actuators, and in particular to a linear voice coil actuator with planar coils.
Two different variations of a moving coil linear actuator with interleaved magnetic circuits that are disclosed in U.S. Pat. No. 4,808,955, issued to BEI Electronics, Inc., are depicted in FIG. 5 and FIG. 7 of that patent. These figures are reproduced as FIGS. 6 and 7 of the present application. A field assembly of such an actuator consists of a plurality of magnets of alternating polarity and of the same or different widths in the direction of motion that are attached to the field blanks (return paths), and a plurality of individual coils located in the cavities between the magnets.
A disadvantage of the above design is that the height of the resulting actuator is large.
The above and other disadvantages of prior moving coil actuators are overcome by the present invention of a linear voice coil actuator including a plurality of field subassemblies each comprising a field blank, wherein at least a first one of the plurality of field subassemblies includes a plurality of magnets of alternating polarity positioned on the field blank to form interleaved-magnetic circuits in a direction of motion of the linear voice coil actuator; and further wherein the plurality of field subassemblies are positioned with respect to one another to form a gap between the first one of the plurality of field subassemblies which includes the plurality of magnets, and another of the plurality of field subassemblies, and a coil assembly that includes coils positioned in a plane within the gap, wherein the plane is substantially parallel to the direction of motion of the linear voice coil actuator.
The magnets of alternating polarity can have the same or different widths in the direction of motion, and the magnets may be spaced apart or in contact with one another.
The field blanks may further include flux path sections positioned to provide, for each of the magnets of the first one of the plurality of field subassemblies and a corresponding portion of a field blank of another one of the plurality of field subassemblies positioned across the gap from the magnet, a flux path through the field blanks perpendicular to the direction of motion of the linear voice coil actuator.
In one of the embodiments of the present invention, first and second ones of the plurality of field subassemblies each include the plurality of magnets of alternating polarities, so that pairs of magnets of opposite polarity from the first and second ones of the plurality of subassemblies are separated by the gap, and further wherein the field blanks further include flux path sections positioned to provide, for each of the pairs of magnets of opposite polarity that are separated by the gap, a flux path through the field blanks perpendicular to the direction of motion of the linear voice coil actuator.
It has been discovered that the inclusion of these above mentioned flux path sections permits the height of the actuator of the present invention to be largely independent of the length of the magnets which are employed. Unlike the previous actuator structures which would typically require an increase in back iron width to accommodate an increase in magnet length in the direction of motion, the present invention does not.
As will be appreciated by those skilled in the art, the above structure can provide an actuator having a substantially reduced height.
These and other advantages and features of the present invention will be more readily understood upon consideration of the following detailed description of certain preferred embodiments of the invention and the accompanying drawings.